Millimeter waves refer to electromagnetic radiation having a wavelength range from about 1 mm to about 10 mm. The corresponding frequency range for millimeter waves is from about 30 GHz to about 300 GHz. The wavelength range for the millimeter waves occupies the highest frequency range for microwaves, and is also referred to as extremely high frequency (EHF). The frequency range for the millimeter waves is the highest radio frequency band, and the electromagnetic radiation having a higher frequency than the millimeter waves is considered to be a far end (a long end) of the infrared radiation.
Millimeter waves display frequency-dependent atmospheric absorption due to oxygen and water vapor. The absorption coefficient for oxygen in atmosphere ranges from about 0.01 dB/km to about 10 dB/km, and the absorption coefficient for water vapor in atmosphere ranges from about 0.03 dB/km to about 30 dB/km. Due to the atmospheric absorption, the strength of a millimeter wave signal decreases more with distance than radio frequency signals at lower frequency.
While attenuation characteristics of millimeter waves limit the range of signal communication, the rapid signal attenuation with distance of the millimeter wave also enables frequency reuses. In other words, an array of millimeter wave signal transmitters may share the same frequency range for a subset of millimeter wave signal transmitters that are separated from each other by a sufficient distance. For this reason, millimeter waves are employed for short range radio communication including cellular phone applications.
The capture of millimeter wave signals poses a unique difficulty due to the short wavelength of the millimeter wave signals. While manufacture of an antenna for the millimeter waves is straightforward since the dimensions of the antenna to be employed for capture of the millimeter waves is in the range of a few millimeters, guidance of the signal from the antenna through a signal transmission line to a transceiver introduces a series of signal reflections at each connection at which the impedance of the components is not matched.
Prior efforts to attach a millimeter wave antenna to a semiconductor chip through a C4 pad or a wirebond pad have resulted in mismatched impedance at the interface between the antenna and the semiconductor chip, which is typically the C4 ball or the wirebond pad. Further, aligning a reflector plate, which is necessary to increase efficiency of the antenna, to the semiconductor chip and the antenna to provide structural integrity is a challenging task.
Incorporation of a millimeter wave antenna into a wiring level dielectric material layer on a semiconductor chip has resulted in poor performance since the distance between the antenna and the reflector plate needs to about the quarter wavelength of the millimeter wave, which is in the range of hundreds of microns, and the total thickness of a metal wiring structure in conventional semiconductor chips is from several microns to about 20 microns. Without a sufficient volume to incorporate a functional reflector plate, any prior art integrated antenna in a semiconductor chip displays poor signal capture efficiency, rendering such an antenna inefficient.
In view of the above, there exists a need for a structure incorporating a transceiver, a millimeter wave antenna, and a reflector plate that captures millimeter wave signals effectively and routes the signal to a transceiver on a semiconductor chip with minimal signal loss.
Further, there exists a need for methods of manufacturing such a millimeter wave antenna.